How to choose courses in college when uncertain what career to chose?

I’m assuming you are referring to choosing A Level or BTEC Courses.
The best advice is to choose subjects that you’ll enjoy and you’ll be good at.
Both A Level and BTEC course can be very intense and you it’s much harder to do well in a subject that you don’t absolutely love.
Some people opt for all sciences and maths or all humanities. This is usually because they are following their strengths. Others choose to mix and match based on what they like.
However there are some subjects that complement each other and it’s useful to study these together. For example, it’s harder to get a top grade in A Level Biology if you aren’t studying chemistry or maths. That’s not to say that it’s impossible but there is overlap between these subjects.
You should also take into consideration your target grades for GCSE. Most sixth form and colleges ask for a grade 6 in that subject and a 4 or 5 in English and Maths.
It’s also useful to talk to the teachers who teach the course to get some information about what it’s like and what the challenges are. As well as that you can speak to year 12 or 13 students at open evening or at your school.
Don’t worry about not knowing what career you want to do. Most people don’t and that okay. Just be aware that if there is something really specific you wish to do eg. Medicine, then there are subjects that you should pick to study. If not, follow your strengths and what you enjoy.
I teach A Level Biology and am more than happy to talk about that or science A levels or BTEC Applied science.
Good luck.